You are not legally required to disclose your HIV status to your dentist. However, if your HIV status is relevant to the treatment you are obtaining, then disclosing your status may lead to the best outcomes. Ideally, try and find a dentist who is used to dealing with HIV positive patients so that you will feel comfortable disclosing your status to them. Your HIV specialist doctor may be able to recommend a dentist.
Source: HIV/AIDS Legal Centre, Sydney http://halc.org.au/publications/guides-to-hiv-and-the-law/